Photographic development by ferrous alkaline solutions



Patented Nov. 9, 1948 PHOTOGRAPHIC DEVELOPMENT BY FERROUS ALKALINE SOLUTIONS Thomas H. James, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application October 26, 1946, Serial No. 106,073

1 5 Claims. 1

This invention relates to photography and particularly to photographic development by alkaline ferrous iron solutions.

The development of exposed silver halide emulsions with ferrous salts such as ferrous oxalate is well known. Ferrous oxalate and other ferrous salts have been used in acid solution to develop silver halide emulsions by reducing the exposed silver halide to metallic silver. Such solutions have been used only in the acid or neutral state.

I have found that exposed silver halide may be developed with a solution of a ferrous salt of suitable alkalinity and that such development produces a ferric oxide image along with the metallic silver image. The silver may then be removed leaving the ferric oxide image in the developer layer.

The solution which I propose to use for development of an exposed silver halide emulsion layer preferably consists of suitable concentrations of ferrous sulfate and potassium oxalate in a solution made alkaline with borax or other alkali to a pH of about 8 or more. Any soluble ferrous salt not involving a complex ion may be employed such as ferrous sulfate or ferrous chloride. Any soluble oxalate such as sodium oxalate or potassium oxalate is suitable. While the function of the oxalate is not entirely clear, I believe that without the oxalate, ferrous hydroxide is formed in solution and this does not penetrate the emulsion layer sufficiently to achieve satisfactory development. While ferro-oxalate ions may be produced in the alkaline solutions containing low or moderate concentrations of oxalate ions, it is unlikely that the ferro-oxalate ion is the principal developer in such alkaline solution. The alkaline ferrous solutions therefore differ from the conventional acid ferro-oxalate developers in which the ferro-oxalate ion is the active developer.

The developing solution may also contain a small amount of restrainer such as potassium bromide as well as other agents used in developers of this type.

The pH of the developer is an important factor in my method. The pH should be above about 8 and as the pI-I increases, additional amounts of oxalate should be used in the solution to prevent premature formation of ferrous hydroxide. At pH 8.8 good images were obtained at concentraticns of potassium oxalate of from 10 grams to 100 grams per liter of developing solution.

It is preferable in my process to carry out the development in an atmosphere free of oxygen.

Ferric oxide images of good quality were obtained when development was carried out in suitable solutions which had been freed from oxygen and maintained under an atmosphere of oxygen-free nitrogen during development. Weaker images were obtained by development in solutions made up without precautions to exclude oxygen and used in air.

The following solution is suitable for development of an exposed silver halide emulsion according to my invention:

Grams FeSO4.7I-I2O 2.78

I. 2C2OA..H2O 37.0

Potassium bromide 0.4

Borax to produce pH of about 8.8. Water to 1 liter.

The silver image produced by development may be removed with the usual ferrocyanide-hypo bleach.

The ferric oxide images produced according to my invention are useful in a number of ways. They may be converted into a ferric ferroci anide image or used as a mordant for various anthraquinone and acid mordant dyes. They may also be used for the production of dyes of the naphthol green B type by reaction of the ferric oxide with dinitro-resorcinol, a-nitroso-o-naphthol, etc., or for the production of black images by treatment wth tannin or logwood. If the silver image is allowed to remain in the emulsion layer, the ferric oxide may be used in combination with the silver image, for sepia toned prints.

It will be understood that my invention is to be taken as limited only by the scope of the appended claims.

I claim:

1. The method of forming a ferric oxide image in a silver halide emulsion layer, which comprises exposing said layer and developing it with an alkaline solution of a soluble ferrous salt and a soluble oxalate in an oxygen free atmosphere, said solution having a pH of at least approximately 8.

2. The method of forming a ferric oxide image in a silver halide emulsion layer, which comprises exposing said layer and developing it with an alkaline solution of a soluble ferrous salt and a soluble oxalate in an oxygen free atmosphere, said solution having a pH of at least approximately 8, and removing the developedsilver and unexposed silver halide from the layer.

3. The method of forming a ferric oxide image in a silver halide' -emulsion layer which comprises exposing said layer and developing it with an alkaline solution of ferrous sulfate and potassium oxalate in an oxygen-free atmosphere, said solution having a pH of at least approximately 8.

4. Themethod v,ofiorming aierriotoxide image in a. silver halide .ilayer which comprises exposing said layer and developing it with an alkaline solution containing ferrous sulfate and from 10 grams to .100 grams per liter of potassium oxalate in an oxygen-free atmosphere, 'sa'idsolution having a pH of approximately 8.8.

5. The method of forming a ferric oxide image in a silver halide layer which room-prises exposing said layer and developing it with an alkaline solution containing ferrous sulfate and from 10 grams to 100 grams per liter of potassium oxalate in an' oxygen-free atmosphere, said solution having 'a pH of approximately 8.8, and removing the developed silver and unexposed silver halide from the layer.

THOMAS H. JAMES.

REFERENCES 'GITZE'D The following references are of record in the ..file of this patent:

UNIT-ED STATES PATENTS 'XXVII, 'l'880ypages 2'79 and 280 cited. 

